The quadrupole time-of-flight mass spectrometer has become one of dominant commercial mass spectrometers due to its characteristics of speediness, high resolution and mass accuracy, high stability and repeatability. Mass spectrometers are always provided with a gas chromatography or a liquid chromatogram in the front so as to pre-separate a complex sample. In recent years, the coupling between the ion mobility spectrometry technology and mass spectrometry has gained a significant development. Due to the orthogonal separation characteristic for the ion mobility technology and the chromatography technology, the separation capability and peak capacity of the chromatograph-mass spectrometry analysis may be greatly enhanced. A plurality of kinds of ion mobility spectrometry technologies exist currently, wherein a drift cell mobility spectrometry technology under a lower atmosphere pressure (generally 1 torr-4 torr) is widely applied. Its working manner matches well to the modern quadrupole-time of flight mass spectrometer. Therefore, the drift cell-quadrupole-time of flight mass spectrometry almost becomes a standard configuration of a research-level instrument.
The current drift cell—quadrupole-time of flight mass spectrometer, or a drift cell-time of flight mass spectrometer, generally has the following problems, as described in the literature J. Am. Soc. Mass Spectrom. (2014) 25: 563-571: (1) since the resolving power of a drift cell is proportional to the square root of the length, the length of the instrument is usually large to make sure high resolving power, which is not convenient for being used in a common lab; (2) in many cases, e.g., a sample with a very low concentration but relatively simple compositions, the ion mobility separation is not necessary and a mode with only quadrupole-time of flight mass spectrometer is enough. However, in the existing apparatus and method, ions still have to pass through the drift cell; usually, the drift cell has a very low transmission efficiency, causing a significant sensitivity loss; (3) a high drift voltage needs to be applied across the drift cell; therefore, its upstream or downstream devices need a voltage of a higher amplitude so as to drive the ions, which is not only highly demanding on the power supply, but also easily causes electrical breakdown. Therefore, a novel ion mobility spectrometry apparatus and method are desirable to solve the problems above.